The invention relates to a method for monitoring the location of the edges of material in strip form.
In German Patent No. 30 32 950, an apparatus for evaluating electro-optically generated raster pictures is described, in which the location of a strip is determined by means of a video camera which generates a continuous image of a strip edge to defect a contrast jump for the purpose of regulating the running of the strip. For the evaluation, such raster picture is sampled line by line and in every line, the raster picture elements up to the chosen contrast jump are counted by means of a picture element counter. As a function of the latter's reading, a command signal for guiding the position of the strip into the desired position is formed. It is further stated in this patent the optical determination of the strip position it is difficult to assure sufficient contrast at the strip edges in the entire temperature range from about 20.degree. to more than 1000.degree. C. If the bright/dark contrasts are too weak, it could happen that the latter are no longer detected by the image converted so that measurement errors result which affect the proper evaluation. If, for instance, no contrast jump is determined in several lines of the raster pictures, this can be interpreted in the sense that the visible area of the strip covered by the camera is entirely covered up, or that the strip is not visible or does not exist at all.
Furthermore, contrast jump which occur within or without the strip due to contamination or by reflections can be evaluated in the sense that the strip edge is not straight, i.e., for instance, a part thereof is ragged or the running of the strip shifts in the visible range if more extensive contamination is the cause. With the known apparatus, such faulty evaluations are avoided by means of a second counter which causes a sort of averaging of the information over the course of the edge. Evaluation of a non-linear course of the edge such as occurs, for instance, in the case of melts, is not possible with the known apparatus.
In the manufacture of plate glass, the trailing edges of the liquid glass are monitored for determining and monitoring the strip thickness. To this end, a picture of the edges can be taken with a television camera and displayed on a monitor where it is observed by the operating personnel and monitored in accordance with subjective criteria. For easier operation, the liquid glass is observed not directly at the exit, but several meters thereafter so that disturbances are leveled out with a long delay.